Role of Musculoskeletal Ultrasonography in Evaluation of Knee Emergencies

Abstract

The knee is vulnerable to a wide variety of acute and chronic injuries sustained during sporting activity. Acute knee injuries most frequently involve the bone, menisci, articular cartilage and ligaments. They are particularly common in sports involving twisting movements and sudden changes of direction. Examples include soccer and rugby, skiing, basketball and volleyball. The knee transmits considerable forces and repetitive injury particularly to the cartilage and tendons is common, especially in sports involving running and jumping (Hopper and Grainger, 2010). Diagnosing trauma comprises a major part of musculoskeletal radiology. In fact, since the advent of magnetic resonance imaging, the role of the musculoskeletal radiologist has expanded greatly. Not only is musculoskeletal imaging important in diagnosing fractures and dislocations, but soft tissue injury and internal derangements of joints have become as important, if not more important, as imaging osseous trauma (Reinus, 2010). In the last decade, musculoskeletal imaging has rapidly expanded due to the imaging capabilities of magnetic resonance imaging and ultrasound (Tan et al., 2003). Musculoskeletal ultrasound has shown considerable expansion in the last few years. The main reasons to explain this development are: better quality of images due to technical improvement (development of high-frequency transducers, refined focusing and sensitive color and power Doppler technology) and growth of interest in low-cost imaging modalities due to economic motivation (Bianchi et al., 2002). Sonography is an attractive tool for the diagnosis of musculoskeletal conditions. The clinician can evaluate the anatomic segment during active and/or passive flexion and extension maneuvers, and its real-time capability allows imaging in positions that trigger symptoms. Scanning the contralateral asymptomatic extremity can be used as a reference for normal anatomy in a given patient (Hashefi, 2009). Indications for ultrasound of the knee vary depending on the experience and knowledge of the sonographer and availability of competing imaging methods. In general, ultrasound performs best in the evaluation of a superficial structure where there is a focused clinical question (Jacobson, 2008). One of the most common indications for ultrasound of the knee is to determine the cause of posterior knee or calf pain or mass, in particular, the presence of a Baker’s or popliteal cyst. Ultrasound is helpful in that a Baker’s cyst can be diagnosed or excluded, and complications of a Baker’s cyst, such as rupture, can also be assessed. Ultrasound and color or power Doppler imaging can exclude deep venous thrombosis and popliteal aneurysm as causes for calf symptoms (Friedman et al., 2003). Another common indication for knee ultrasound involves the extensor mechanism of the knee and surrounding soft tissues and bursae. For example, the specific question of a quadriceps or patellar tendon tear can be addressed with ultrasound. Ultrasound can be used to evaluate other superficial soft tissue structures about the knee. For example, the medial collateral ligament and the lateral collateral ligament can be visualized and assessed for abnormality. These structures are less commonly abnormal and a clinical history with specific clinical questions helps to guide ultrasound assessment (Friedman et al., 2003).